1. Field of the Invention
The present invention relates to image processing, and, in particular, to encoding video images.
2. Description of the Related Art
In teleconferencing applications, video sequences typically consist of a two distinct layers: a background layer and a foreground layer. The background layer consists of the static objects in the scene that ideally should be coded and sent to the receiver only once. Conversely, the foreground layer consists of objects that move and change shapl as time progresses. By concentratinig bit allocation on pixels in the foreground layers, more efficient video encoding can be achieved. To achieve this goal, some video coders perform foreground/background segmentation to determine which portions of the video images correspond to foreground and which to background. In general, background regions correspond to portions of the scene that do not significantly change from frame to frame.
Accurate foreground/background segmentation can be thwarted when the video images are generated by a video camera that performs automatic gain control (AGC). AGC is performed to ensure that the subject (i.e., a foreground object) falls well within the dynamic range of the camera. Unfortunately, AGC causes interframe differences to occur in regions that are spatially static (e.g., background regions). This can result in undesirable increases in the bitrate. It can also lead to misidentification of background regions as being part of the foreground.
What is needed is a video encoding scheme that addresses the bitrate and foreground/background segmentation problems created by using video cameras with automatic gain control.
It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the known art and to provide an improved scheme for encoding video streams generated by video cameras operating with automatic gain control.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.